An important function in present day agricultural practice includes controlling weeds, insects, and other pests that are injurious to productivity and crop growth. For effective weed and pest control, a number of chemical preparations are available in dry granular form for application to the ground or to the plants. These dry granular chemicals can be applied to the soil before, during, or after planting. They can also be applied directly to the growing plants long after the planting operation.
In order to be effective, the chemical must be applied to the target in the appropriate dose. The target can be soil or plants extending across the entire field, or only across selected areas such as furrows, bands, and isolated spots. The optimum dose is one that is sufficient to cause the effect desired but no more. From the standpoint of the chemical user, that person wants to gain the maximum benefit from the minimum cost to maximize the economic gain. From the standpoint of the environment, keeping the dose as low as possible minimizes the chance of the chemical affecting nontarget organisms. In most situations, uniformly distributing the optimum dose on or in the target allows the minimum dose to have the maximum effect. If some areas of the target receive a higher than optimum dose, usually no additional benefit is gained and additional cost is incurred through waste. If some areas of the target receive a lower than optimum dose, usually the desired effect is reduced and often will not occur, the net result being lesser productivity from waste of the chemical.
Delivering the optimum dose to the target has three aspects. First, the chemical formulation, whether wet or dry, must be substantially homogeneous. Second, the proper amount of chemical must be metered to the target. Third, the metering of the chemical must be substantially uniform to achieve the desired concentration.
It will be appreciated that such chemicals are at least mildly toxic and must therefore be handled and distributed with care. Leakage of such granular chemicals from the applicator at places other than the target areas, presents a hazard to persons coming into contact with such chemicals until such time as the chemicals are incorporated into the soil, absorbed by the plants, or otherwise rendered harmless. This is another reason why precise metering and control of the chemicals are desirable.
A variety of applicators for this purpose have been available heretofore. Such applicators are usually provided with metering apertures at the bottom of a hopper through which material is discharged by means of gravity and a feed rotor located inside the hopper above the apertures. U.S. Pat. No. 3,776,430 to the assignee hereof shows one such prior device. U.S. Pat. Nos. 3,128,921 to Henderson and 2,784,881 to Hines are also representative of the prior art in this regard. The Henderson and Hines patents disclose applicators which feed the material from the hoppers onto discharge rolls. The feed rotors are connected to their respective discharge rolls for rotation in opposite directions.
In many of the prior applicators, feeding of the granular material is stopped both by closing the metering apertures and by arresting rotation of the feed rotor to prevent undue agitation and thus damage to the material which would otherwise occur during rotation of the feed rotor while the apertures are closed. When transporting the device from one field to another, the common practice heretofore has been to disconnect the feed rotor from its drive mechanism without closing the discharge or metering apertures, however, this still results in leakage, waste and thus expense.
There is thus a need for an improved applicator which incorporates a speed compensator to effect better control of the material being discharged.